Martha Louise shows where her heart lies - with her royal mum

As Norway celebrated Queen Sonja's 70th birthday her only daughter, Princess Martha Louise, made a loving gesture of her own, donning a heart-shaped brooch containing an image of her mum. The fashion-forward 35-year-old was clearly in a sentimental mood as she pinned the old-fashioned tribute, framed in multi-coloured diamonds, onto her striking purple outfit.

It's not the first time this year mum-of-two Martha Louise, who's married to author Ari Behn, has adopted a striking heart theme. Back in February, on the eve of Valentine's Day, she picked out a heart-patterned coat to wear to Oslo Fashion Week.

After several days of festivities to mark the Queen's landmark birthday, it's now back to business as usual for the Norwegian royals. On Wednesday Martha Louise - a children's writer - is expected to attend an annual track and field event in Oslo.